A lap is a surface (usually horizontal) created between the knee and hips of a biped when it is in a seated or lying down position. The lap of a parent or loved one is seen as a physically and psychologically comfortable place for a child to sit.[1][2] In countries where Christmas is celebrated, it has been a tradition for children to sit on the lap of a person dressed as Santa Claus to tell Santa what they want for Christmas, and have their picture taken, but this practice has since been questioned in some of these countries, where this sort of contact between children and unfamiliar adults raises concerns.[3]

Among adults, a person sitting on the lap of another usually indicates an intimate or romantic relationship between the two; this is a factor in the erotic activity in strip clubs known as a lap dance, where one person straddles the lap of the other and gyrates their lower extremities in a provocative manner.[4]

The lap can be a useful surface for carrying out tasks when a table is not available.[5] The laptop computer was so named because it was seen as being able to be used on the user's lap,[6] but a study by State University of New York researchers found that heat generated from laptops can increase the temperature of the lap of male users when balancing the computer on their lap, potentially putting sperm count at risk. The study, which included roughly two dozen men between the ages of 21 and 35, found that the sitting position required to balance a laptop can increase scrotum temperature by as much as 2.1 °C (4 °F).[7] A later 2010 study of 29 males published in Fertility and Sterility found that men who kept their laptops on their laps experienced scrotal hyperthermia (overheating) in which their scrotal temperatures increased by up to 2.0 °C (4 °F). The resulting heat increase, which could not be offset by a laptop cushion, may increase male infertility.[8][9][10][11][12]